The doubly fed induction generator (DFIG)-based wind energy conversion system (WECS) suffers from voltage and frequency fluctuations due to the stochastic nature of wind speed as well as nonlinear loads. Moreover, the high penetration of wind energy into the power grid is a challenge for its smooth operation. Hence, symmetrical faults are most intense, inflicting the stator winding to low voltage, disturbing the low-voltage ride-through (LVRT) functionality of a DFIG. The vector control strategy with proportional–integral (PI) controllers was used to control rotor-side converter (RSC) and grid-side converter (GSC) parameters. During a symmetrical fault, however, a series grid-side converter (SGSC) with a shunt injection transformer on the stator side was used to keep the rotor current at an acceptable level in accordance with grid code requirements (GCRs). For the validation of results, the proposed scheme of PI + SGSC is compared with PI and a combination of PI with Dynamic Impedance Fault Current Limiter (DIFCL). The MATLAB simulation results demonstrate that the proposed scheme provides superior performance by providing 77.6% and 20.61% improved performance in rotor current compared to that of PI and PI + DIFCL control schemes for improving the LVRT performance of DFIG.
The world is experiencing wind energy with high penetration causing multifold increase in the wind energy capacity [1]. The wind energy conversion system (WECS) not only aims at maximizing the power at variable wind speeds but it should also provide good power quality [2]. Typically, due to its elegant performance with variable wind speeds, partial scale convertors, effective active and reactive power transfer and control capacities, low equipment costs and reduced power losses, DFIG has been chosen to maintain maximum power output [3]. It covers more than 50% of worldwide onshore large-scale wind power installations [4], [5]. The main problem with WECS on a converter basis is that frequency and voltage variations [ 6-7] are driven by the variable wind speed. Large oscillations in wind speed as stated above significantly change the power output as a result of irregular environmental conditions [8]. For the operational efficiency and reliability, DFIG based wind power generation must be capable of staying with power grid and contribute towards voltage stability. Since, DFIG uses a bidirectional VSC which enables it to receive and transfer reactive power [9-10].
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